1. Field of the Invention
The present invention relates to a constant voltage generating circuit, more particularly, to a constitution of a circuit which feeds a constant voltage to a bipolar complementary metal oxide semiconductor (Bi-CMOS) circuit using a plurality of power supply voltages.
2. Description of the Related Art
A typical Bi-CMOS device including bipolar transistors and MOS transistors by mixture in an identical chip is usually constituted to be operated by a single power supply voltage fed from the outside of the chip. Also, in the case of use of a plurality of power supply voltages as well, some of the power supply voltages are fed from the outside of the chip. In this case, the other power supply voltages are fed by a voltage generating circuit which is provided within the chip and receives the external power supply voltages. Also, since dispersion between each power supply voltage is not concerned with each other, it becomes necessary to sufficiently assure an operation margin (voltage values necessary for the exact and reliable operation of the device). To this end, the voltage generating circuit must feed a constant voltage or voltages at all times even if the external power supply voltages fluctuate due to a change in temperature, and the like.
In a known voltage generating circuit, however, the above ideal constitution has not been proposed. Problems in the prior art will be explained in detail later.